1. Field of the Invention
This invention relates to a method of engraving materials using a laser and a mask which is spatially removed from the parts to be engraved.
2. Prior Art
It is well known that lasers can develop sufficient power densities to vaporize certain materials. Lasers such as high-power carbon dioxide lasers can vaporize many materials such as wood, plastic and rubber, relatively efficiently. Once the output from a laser is focused to a power density greater than approximately 10,000 watts per centimeter, it is possible to remove material from the surface of organic solids even when the laser beam is rapidly scanned across the surface. Of course, areas not struck by the laser beam are not vaporized. The use of the laser offers the potential of producing very intricate engravings in the proper material. One method of selectively engraving areas of a material is to manipulate the laser beam along the areas to be removed, using the laser much like a wood carver uses a knife. However, this method does not lend itself to mass production.
Another method of laser engraving uses a thin metal mask which is placed in contact with the part to be engraved. As the laser beam scans back and forth the beam penetrates to and vaporizes the part to be engraved only in the area which is not protected by the metal mask. Inasmuch as metals can withstand high laser power densities without being damaged, metal masks are not affected by the laser. This process, however, cannot produce detailed contours; moreover this process is not well suited for mass production inasmuch as fragile metal masks must be placed on and removed from the materials which are to be engraved.